Pem-type electrolyzer stack for operation at high pressure

ABSTRACT

Electrolyzer module comprising a front plate, end plate enclosing an anode cavity, and a cathode cavity.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority under 35 U.S.C. 371 to International Patent Cooperation Treaty Application Serial No. PCT/EP2012/072982 filed Nov. 19, 2012 and entitled “PEM-TYPE ELECTROLYZER STACK FOR OPERATION AT HIGH PRESSURE,” which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

A PEM Electrolysis module is a filter-pressure design (STACK) collected from the cells, sandwiched between the end plates with bolts. An Electrolyzer has an internal communication system associated with the external system of water regime providing and gas separators. Internal communication is facilitated by channels that are formed by the connections of individual parts by doing in these parts a number of coaxial holes. Elements of the cells are sealed with gaskets from made of fluorine rubber.

STATE OF THE ART

The improvement and optimization of a PEM electrolyzer efficiency and operative life operating at high pressures is linked to the following:

Membranes with low ion-exchange capacity

The technology of the MEA manufacturing with structural improvements in order to increase contact with the current collectors

Optimization of the mesh elements design, gaskets, bipolar plates, as well as system of supply and distribution of reagents to the cell contours

Providing a more uniform distribution of water on the active surface of the electrolyzer cells

Providing rapid removal of electrolysis gases from the cathode and anode spaces

Providing a minimum electrical contact resistance of electrolysis cell elements and minimum degradation

Hydrogen occurrence in oxygen may in some cases accompanied by decreasing of a current efficiency (up to 50% at smaller currents) relative to theoretical value, which is obtained at the assumption of losses from a crossover. Hence, processes, which lead to hydrogen formation in anode area, may be electrochemical character and directly accompany anode processes of water decomposition. Hydrogen concentration in electrolytic oxygen cannot be caused only membranes gas permeability; It is possible that the hydrogen in electrolyzer anode space is formed as a result of electrochemical processes directly in anode catalyst layer or corrosion processes on electrolyzer design elements. It should be noted that the specific reasons for such processes to the end and not yet clarified the issue continues to be relevant.

Uniform distribution of water on the active surface of the cell provides a uniform release rate of electrolysis gases formation. This eliminates the possibility of the formation of stagnant zones, and increases efficiency and life of work, improves the purity of electrolysis gases and prevents accidents related to local heat, causing destruction of the elements of MEA.

Quickly remove of electrolysis gases from the cathode and anode spaces provides increased water content in the cathode and the anode space of the electrolyzer, which contributes to improving the efficiency of electrolysis.

The minimum contact resistance of electrolysis cell design elements at operating conditions provides the best electrical characteristics of the cell and, consequently, increases its efficiency as a whole.

For obtain of pure electrolytic gases it is necessary to improve MEA manufacturing techniques (improve the homogeneity of the catalytic layers structure, clarification of requirements for the degree of dependence of membrane gas permeability from temperature has exponential increase and increases approximately by 5 times at increase temperature from 40° C. to 80° C. while hydrogen concentration in anode area almost does not depend from temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings illustrate a preferred embodiment of the invention, which should not be interpreted as restricting the scope of the invention, but just as an example of how the invention can be embodied.

FIG. 1 Shows the electrolysis module in the backpressure case where the electrolyzer stack, is located.

FIG. 2 Shows the end plate with a handing out channels to be implemented in the present invention.

FIG. 3. Shows a gasket with the holes and channels with conical to be implemented in the present invention

FIG. 4. Is a representation of a mesh insert to be implemented in the present invention.

FIG. 5. Show the mesh insert with dividing walls to be implemented in the present invention.

FIG. 6. Show the water and gases flows in the electrolisis stack with the components of the present invention.

DETAILED DESCRIPTION

The invention is related to several improvements in the design and construction of components and manufacture techniques of the PEM electrolyzer stack components that solve the majority of the technical issues that have influence in the gas production at high pressures up to 500 bars. The invention provides a PEM electrolyzer working at high pressure, placed in a backpressure case (FIG. 1). The case is filled by an inert gas (or hydrogen) at pressure, which corresponds to the pressure inside the electrolyzer. This design and operating mode has been described in our Patent P200900163.

Because the distribution and collection of reagents in the electrolysis module is made from the front side, there is a need to direct flows towards the rear of the electrolysis module. To do this, the invention presents an end plate with milled grooves, (FIG. 2) with this end plate design, distribution and collection of reagents is performed from the two sides of the plate. In order to obtain a more uniform distribution of water on the active surface of the cell and more efficient removal of electrolysis gases from the cathode and anode space by optimization of sizes, amount and configuration of the input and output of gases and water, the invention presents in a particular embodiment, a configuration of the gaskets with conical windows for inserts of a conical shape, (FIG. 3). The configuration of distributing holes in gaskets, depends on the amount of generated gas (ie, the number of cells in the electrolysis module and pressure) can be made from two to eight over-sized holes. The size of the slot channels of the upper and lower inserts made different: in the upper groove gasket are installed inserts with E=1.00 mm tp 2,8mm, in the lower grooves are installed inserts with E=0,70 mm to 1.50 mm. This allows to provide the necessary backpressure to improve the uniformity of reagents and flow distribution on the cross sections of electrolysis cells.

To provide uniform water distribution in the inner cavities of the electrolysis module cells and to reduce the “stagnant” zones in gasket construction in a particular embodiment, the invention is provided with slotted holes that form additional cross- cutting channels. To reduce dead zones, two to four channels , depending on the amount of generated gases, for distribution and collection reagents are provided, and the holes have a shape such as to direct the flow towards the gaskets corners. (FIG. 3)

To reduce corrosion at the center of the bipolar plates and the corners of porous current collectors, the inner corners of the gasket windows are rounded, with a predetermined curvature radius

Deposition of the catalytic layer directly on the membrane results in improvements in the homogeneity of the catalytic layer's structure, highly degree of purity of reagents and materials, specially when the process is carried on with a current density of 1 A/cm² and voltage lowered to 100 mV for the cell, or at a current density of 2 A/cm²-for 200 mV. Hydrogen concentration in electrolytic oxygen falls under this conditions approximately a 10%.

In order to lower the electrical contact resistance of the mesh inserts of the electrolyzer (FIG. 4) The first and third layer of the grids are immediately rolled “in size” and have a smooth surface, and the second layer, located between them, has a different thickness without smooth surfaces After welding of the grid layers “rolled on rollers to the desired size”, which allows improving the contact resistance between the layers of grids and reduces the contact resistances. With the use of this technology object of the invention we reduce the contact electrical resistance of the electrolysis cell construction is reduced from 25 mQ/cm² to 15 mQ/cm², which corresponds to the decrease in cell voltage at a current of 1 A/cm² at 10 mV.

Another variant of the mesh inserts construction described above (FIG. 5) may be with dividing walls for optimization of water distribution. The presence of walls directs the water flow to the right direction and eliminates the appearance of stagnant zones. This design is more effective in cells with a large work surface. In FIG. 6. is presented the scheme of water and gas flows inside the electrolysis stack manufactured with the elements of the present invention. Water is supplied to the anode channel through 3 lower front flange fittings. After that, water is decomposed on the membrane and oxygen and part of remaining water passes to the rear end plate at its upper part, and through channels made in the end plate, turns to the side of the front flange and is expelled through two upper lateral connections. Water is supplied through 2 bottom side connections to the cathode cavity of the electrolysis stack ,then passes to the back plate where the flow turns in the opposite direction and is distributed over the cathode cavity. The resulting decomposition hydrogen input into the upper hole of the electrolyzer stack components and comes out through the top 3 fittings in the front flange. 

1-7. (canceled)
 8. An electrolyzer stack, comprising: a. a first end plate defining a first end of the stack; b. a second end plate defining a second end of the stack; c. a plurality of flange fittings; and d. an electrolyzer module disposed between the first and second end plates, the module being configured to decompose water comprising: i. a plurality of channels; ii. a plurality of cells; iii. at least one bipolar plate; iv. at least one anode; v. at least one cathode; and vi. a low ion-exchange capacity membrane; wherein the bipolar plate, anode, cathode and membrane are operationally and fluidically coupled such that water can be passed through the plurality of flange fittings into the module to be distributed evenly throughout the module and through the channels from the first end plate toward the second end plate, and further wherein hydrogen and oxygen can exit the stack and exit the module through the plurality of flange fittings.
 9. The electrolyzer stack of claim 8, wherein the plurality of flange fittings further comprises at least one upper and at least one lower flange fitting; wherein the upper and lower flange fittings are disposed on the first end plate and further wherein the at least one lower flange fitting is configured to pass water into the module and the at least one upper flange fitting is configured to allow hydrogen or oxygen to exit the module.
 10. The electrolyzer stack of claim 9, wherein the first or second end plate further comprises milled grooves.
 11. The electrolyzer stack of claim 8, further comprising at least one gasket.
 12. The electrolyzer stack of claim 11, wherein the at least one gasket further comprises at least one conical window.
 13. The electrolyzer stack of claim 12, further comprising at least one mesh insert.
 14. The electrolyzer stack of claim 13, wherein the electrolysis cell has an electrical resistance of less than 25 mΩ/cm².
 15. The electrolyzer stack of claim 13, wherein the electrolysis cell has an electrical resistance of about 15 mΩ/cm².
 16. The electrolyzer stack of claim 15, wherein the electrolyzer stack is capable of operating at pressures up to 500 bars. 